And so, summer heat begins!

   In case you haven't heard we are on the verge of a prolonged spell of summer heat set to arrive right after the 4th of July. Years ago, it seemed summer would always begin right after the 4th of July in the Spokane however is that really true? According to statistics, perhaps not. Interestingly enough, we can define summer by looking at the warmest 91 (3-month period) of the year which according to our climate statistics occurs around June 16th. Also interesting is the fact, that the beginning of the summer season has been getting later and later each year, however there is a significant amount of disparity when looking at the chart below.  

Also interesting is noting the abundance of red dots since 2000 signifying a warmer than normal summer. Since 2000, 75% of the summers have been warmer than normal with a current streak of 12 warmer than normal summers. Below is a closer examination of that factoid plotted against the 30-year moving average.  The blue line represents the average summer temperature (based on June-August data and not the 91-day period shown above. 

So enough of the summer background, let's take a look at the upcoming forecast and heat-filled details. This burst of heat will arrive care of a very strong ridge of high pressure. If we look at the 500 mb charts (~18,000') in the atmosphere we can see how this scenario is going to play out. On Friday, the ridge will begin to build off the coast and this should begin the heat event.

500 mb heights Friday

By Sunday the ridge will migrate toward the center of Washington ensuring we warm up even further. 

500 mb heights Sunday

By Tuesday the ridge axis shifts into eastern Washington and then the heat will really get going across the Inland Northwest. 

500 mb heights Tuesday

But that's not the end of it, as it looks like the heat will peak on Wednesday or Thursday with the ridge shifting to the Montana/Idaho border. 

500 mb heights Thursday

So how confident are we this scenario is going to pan out? At this point, quite confident. In the past we only had a few weather models at our disposal and run-to-run changes were common, especially at the latter ends of the forecast (for instance days 4-7). However now we utilize ensemble forecasting which takes multiple models (over 100 for the days 1-2 forecast and 100 for days 3-7) and complies them for us. This method can show us the range of possible outcomes and in this upcoming pattern there just aren't a lot of outcomes other than just plain hot. The easiest way to determine how uncertain the forecast is by examining a chart that shows the different model solutions and plotting them on top of one another. 

Let's start by examining the model possibilities for Sunday.  Note the ridge positioned along the West Coast and the pale-yellow shading over the region. The shading represents the differences in the 500 mb heights between the 100 model runs. In this case, the differences are only around 2 decameters, which signifies good model agreement. If you look farther west, over the Gulf of Alaska note the purple shading which signifies large model differences (13 decameters, which is significant). Seeing model agreement only 2-3 days into the forecast isn't unusual, especially for a ridge. 

500 mb ensemble model differences on Sunday 7/7/24

By Tuesday the model differences with the ridge increase, but not by much (only 1 decameter over the Pacific Northwest). This still suggests high forecast certainty. 

500 mb ensemble model differences on Tuesday 7/9/24

By Thursday the model differences increase slightly, but again not to the point where we would think the ridge will be replaced by the offshore trough, delivering cooler weather. All the significant model differences remain on the eastern or western periphery of the ridge. 

500 mb ensemble model differences on Thursday 7/11/24

If we go out even further to next Saturday, there still is a higher-than-normal chance that the ridge is going to stick around, however we'd have to imagine we'd see some cooling by then. 

500 mb ensemble model differences next Saturday 7/13/24

So far, we've only examined the 500 mb heights, which are indicative of sinking air and generally fair weather, but how does that translate to temperatures on the ground?  First, we will examine the mean temperatures forecast by the National Blend of Models. This represents the most likely outcome. 

NBM mean temperature forecast for the Inland Northwest

However, what would we expect if the warmest 25% of the model solutions came to fruition? That would certainly support a historic heat wave. There's no reason to believe this will occur, however it just hints at a possibility. 

NBM 75th percentile temperature forecast for the Inland Northwest

So, what are our chances of exceeding 100°F during the next week or so? It's a done deal for the LC Valley, as well as the Columbia Basin and Okanogan Valley. There's a slightly lesser chance for Spokane, while the "cool" escape will be to Sandpoint. Below is a list of the chances:

Chances of hitting 100°F or hotter

As you can see, the odds are quite good that a large portion of the Inland Northwest will see a multi-day period of triple digit heat. Currently our forecast doesn't suggest we will break any records for consecutive 100°F days however once again we could easily see 4 consecutive days of triple digit heat in Spokane. Something which occurred in both 2021 and 2022 but not many years other than that. The record is 6 set in 1928. 

Other daily records could be broken beginning on Sunday and continuing at least through Thursday. Spokane's records are as follows: 7/7 99°F, 7/8 99°F, 7/9 100°F, 7/10 102°F, 7/11 103°F. All are certainly within reach. We also got the question is Spokane's all-time record in peril? Just 3 years ago Spokane set a new record of 109°F (6/29/2021). While we don't expect to break this record during this spell, it is not a 0% chance. In downtown Spokane, the chance is around 10% on Thursday (in other words 10% of the ensemble model runs are forecasting temps of 109°F or warmer), while at the Airport (the official forecast spot for Spokane) the chance is around 2%. 

Chance of 109°F or warmer on Thursday 7/11/24. 

So far we've discussed the daytime highs which will be trying enough to those who don't tolerate heat well. But we also have to factor in the nighttime lows. Unfortunately, these won't cool off too much either. The table below reveals overnight lows only dipping into the mid 60s to mid 70s for most locations. That means folks without air conditioning will have a tougher than usual time cooling off their houses during the night. And the length of this event will only exacerbate this issue. 

Nighttime low temperature forecasts

If you add these factors together, we are looking at a trying environment for many denizens of the Inland Northwest. We can characterize this using an index we call HeatRisk. By Sunday a large portion of the region will experience Major heat risk which means the heat will impact anyone without effective cooling and/or having access to adequate hydation. 

Sunday HeatRisk

By Tuesday (the last day available for the HeatRisk as of this blog post), we begin to see extreme values popping up around the area. Remember, we expect the heat to peak on Wednesday or Thursday which suggests the magenta will become more widespread. 

Tuesday HeatRisk

Needless to say, we urge all of our friends to take the necessary precautions ahead of time and prepare for this upcoming heatwave. Here are a few hints from the CDC to help you beat the heat. We also want you to treat your loving pets with the utmost care to keep them safe during this heatwave. Please stay tuned to our latest forecast to see how hot it is going to get. 

Safety advice from the CDC and the NWS for you and your pet

A worsening drought over parts of eastern Washington?

   Springtime across portions of the Inland Northwest has been very dry at least compared to climatology. We can measure just how dry using various tools in our meteorological tool box. One of the conventional tools we use is simply looking at precipitation maps across the region. So how have things looked over the past 90 days? 

As you can see things are highly variable across the region. near the Cascades it has actually been quite wet, with precipitation amounts nearly twice the average amount over the past 90 days. Also near the Washington/Idaho border amounts have been close to normal (aside from the southern Palouse, LC Valley, and Blue Mountains). However one area that  stands out is a portion of central Washington in the lee of the Cascades stretching from Omak down to Moses Lake and The Tri-Cities and Yakima areas. Some of these locations have seen only a quarter of the normal precipitation during this period. 

If we add the November precipitation amounts to the mix, the resulting map doesn't look much different for the dry areas. 

So that got us thinking is this a record of some sort? Now granted these statistics are rather arbitrary, After all, who calculates records from 11/23 through 3/21? Not many people, but just for fun we will examine some of these odd records. First we will look at Yakima. 

Yakima, WA precipitation 11/23-3/21

So in fact this is a top 10 driest period for Yakima, but it was actually drier in 2018. Now how about Omak? Not quite top 10 but close. 

And finally lets look at the Ephrata:

Only in 16th place out of the last 70 years and the driest since 2014. So although this is noteworthy, it isn't really a historic dry spell. 

But precipitation alone does not tell the entire story about a dry spell of weather. Other things to take into consideration during this period include; winds, temperatures, relative humidity levels, and solar radiation. All of these parameters will impact the amount of evaporation or evapotranspiration that can take place and how quickly the soils will dry out. That is a lot of information to keep track of, however fortunately we have a relatively new and very useful tool called the  Evaporative Demand Drought Index or EDDI. This takes all the aforementioned parameters into account and states how thirsty the atmosphere is. So what is this index showing for the area? If we go back to November things look particularly bad:

Over the entire Lower 48, no area has seen  more widespread and harsh drying conditions compared to normal. The categories on the map correspond to our typical drought outlooks. In this case the shading over eastern Washington corresponds to an ED4 or an exceptional drought. Does that mean this area is now in an exceptional drought? Not necessarily. A drought is not built on four months of weather alone, but if these trends continue we will certainly be faced with worsening drought conditions over this portion of eastern Washington. Since November here is how the drought monitor has been evolving across Washington.

These images start in the middle of November and advance two weeks at a time. The last image shows the drought conditions as of the middle of March.

Specifically looking at the March 17th the outlook:

This map shows that almost 23% of Washington is in a D1 or moderate drought which just so happens to correspond closely to the first precipitation maps we showed. But what is interesting is the EDDI maps show worse conditions than what's depicted by official drought maps and sometimes this can foretell the trends. EDDI itself is not a drought prediction, but at short timescales (such as what we have shown), it indicates the potential for drought (or trends). So this area certainly bears watching.


So looking past the EDDI values what do the longer range weather forecasts tell us? That is always a tough question to answer, but lets look. The 8-14 day outlook through the beginning of April calls for near normal precipitation and cooler than normal temperatures. Near normal precipitation amounts would certainly help. The cooler than normal readings should also temper the thirstiness of the atmosphere however that could be overcome by having unusually dry air masses in place or prolonged windy conditions.

As for the April outlook, things don't look terrific for a dramatic improvement at this point with below normal precipitation favored at this time with an equal chance of normal temperatures.

And finally, if we want to peer even farther into the future (April-June) the prognostication right now would suggest worsening drought conditions. But we will just have to wait and see.

So what are the ramifications of a drought over the Columbia Basin? While much of the area is irrigated for agriculture, there are areas which also have a considerable amount of sagebrush which could eventually lead to quick burning fires this spring. It could also lead to more blowing dust than normal on a windy day.  Part of this dry area also encompasses some denser fuels both east and west of Omak. Right now the nearest snotels (snow measuring sensors) depict a snowpack around 65%. It's too early to say if this will lead to a busier than normal fire season in these areas as we have found the leading cause of a big fire season is a hot and dry summer.

We will revisit this topic later this Spring to see how things panned out.

UPDATED....Is a significant snow event possible for Spokane,Coeur d'Alene or the Palouse late tonight and tomorrow morning?

So as we talked about yesterday, an unusually tricky weather scenario looks like it will unfold over the Inland Northwest. So what are we fairly certain about? We are fairly confident that a slow moving upper-level low-pressure system will take up residence over the Inland Northwest and produce a band of moderate to locally heavy precipitation. The big questions to answer are where is this band going to set up and will it cool the atmosphere enough that we could see some significant snow. The setup producing the unusual event looks quite similar to what we discussed in our previous blog. We still expect to see strong lifting associated with a slow moving upper level low parked somewhere over eastern Washington. Notice the green shaded area (representing upper-level moisture) remains parked over eastern Washington and the central Idaho Panhandle through much of Tuesday.

500 mb pattern 2am Tue-5pm Tue

The lifting from the low will be accompanied by plenty of moisture and instability which should be perfect for producing a band of precipitation. Just how much precipitation are we talking about? A lot to say the least. The areas in purple represent totals between 0.50-1.00 inches of liquid and the reds and yellows equate to amounts between 1.00-1.50 inches. This is for the 12 hours between 2am through 2 pm Tuesday. Notice the band of heavy precipitation has eeked farther north than what we were looking at in yesterday's forecast and blog.

Latest 12 hr precipitation forecast 2am Tue-2 pm Tue

Previous 12 hr precipitation forecast for 2am Tue-2pm Tue

We still highly suspect that whatever verifies from a precipitation standpoint will more closely resemble the top two panes showing a heavy east-west oriented band vs the more poorly defined precipitation blob in the lower two panes.

Since the forecast is nearing in time we can also use one of our favorite tools called the HRRR (a rapidly updating model that runs hourly and can ingest current weather conditions). Let's see what the latest run of it says. The loop below is a simulation of what the radar is expected to look like. Green and yellow shading indicates where the heaviest precipitation is expected.

Radar simulation for Tuesday morning

So this also boosts our confidence that this event is going to occur. Each subsequent run of this model continues to show a similar radar formation (with small variations in location).

Now the largest problem remains is will the temperatures cool down enough to support snow. The models vary in this regard and there is a fine line as to whether or not snow can fall and then whether it will get heavy enough so it can accumulate on roads. The odds of rain changing to snow over the Inland Northwest look fairly good especially over Idaho and southern Spokane County and northern Whitman County. However a tougher question to answer is will the snow be able to accumulate on the area roads? If the snow gets heavy enough the answer is yes, however if not, most of the accumulations will occur on grassy surfaces. So once again lets look at the plume diagrams to see how much snow 27 different model runs produce over Spokane, Coeur d'Alene and Pullman.

Spokane plume diagram shows snow totals ranging from 0.0 - 2.5" with an average around 0.3" 

Coeur d'Alene plume diagram shows snow totals ranging from 0.0 - 5.3" with an average around 0.8" 

Pullman plume diagram shows snow totals ranging from 0.0 - 3.5" with an average around 0.5" 

Generally speaking, these values are on par with what the models were showing last night, however with the band moving further to the north, the snow totals in Pullman are trending lower. Motorists are still urged to check the latest forecast before venturing out in the morning and be prepared for a potentially snowy commute. Here is our latest snow forecast.

Snow forecast for Tuesday (issued 9 pm Monday )

1145pm Monday Update....the band of precipitation was beginning to take form. Our confidence is growing the moderate to locally heavy precipitation band will develop. Still not sure if heavy snow will accumulate.

1147pm radar imagery. Note heavier precipitation developing between  Davenport and Ritzville. 

Is the end of fire season expected soon?

So while we can't argue that the worst of fire season is behind us, it should be noted there are still fires burning across portions of the Inland Northwest. Here's is what satellite information was showing on the last day of September:

MODIS Visible Satellite Imagery from 9/30/15

While these fires are far from the raging infernos we saw earlier this summer, it's still rather impressive for the end of September or beginning of October.  However, as we all know this year is different. First off, look at these precipitation totals since the beginning of April

Idaho Precipitation % of normal 4/2/15-10/1/15

Washington Precipitation % of normal 4/2/15-10/1/15

That is a lot of red and dark red shading over the Inland Northwest which correlates with meager precipitation amounts ranging 25-70% of normal. That's pretty dry. In fact, since the beginning of April through the beginning of October it was the driest period on record for both Spokane and Boundary Dam, WA (extreme NE corner of the state).

So combine the record dry conditions with nearly record warmth for both sites and it is no wonder the fire season has been so long. Here is a look at the temperatures for both sites.

So obviously record warm and dry conditions led to our active fire season, but unlike a typical year, things just aren't winding down as quickly as we are accustomed to. Climatologically, the days of active fires will be limited. We say that because the shorter days are leading to cooler temperatures and higher relative humidity levels  (both items are generally detrimental to good fire growth) while the chances for measurable precipitation are rising quickly. Climatologically the chance of measurable rain ranges from 20-25% over locations where the fires are currently burning. However by the end of the month those chances nearly double. So despite these facts, look at the latest fire danger ratings for the Inland Northwest:

Current Fire danger ratings

That map shows the fire danger is still high (yellow) or even very high (orange) across a sizable portion of the Inland Northwest, with moderate conditions (light green) found everywhere east of the Cascades. So what does that mean? According to the Wildland Fire Assessment System (WFAS) a high fire danger means, "All fine dead fuels ignite readily and fires start easily from most causes. Unattended brush and campfires are likely to escape. Fires spread rapidly and short-distance spotting is common. High-intensity burning may develop on slopes or in concentrations of fine fuels. Fires may become serious and their control difficult unless they are attacked successfully while small.

So is this danger level unusual for the beginning of October? Since 2006 (earliest year of  the graphical archive), the current fire danger has only been matched one time. That was in 2012. All other years saw low to moderate fire danger ratings across the area.

So what was the fire weather like in 2012? This satellite picture tells the story

MODIS Satellite imagery from 10/4/12

Just like this year, there were quite a few fires burning during the beginning of October. In fact, based on the satellite image, they were much bigger and included the Wenatchee Complex (southwest of Wenatchee) and the St. Mary's Misson Rd fire south of Omak. So what happened that year? The dry weather and fires continued to burn through the middle of the month, but several days of rain (not necessarily heavy) and cooler temperatures put an end to that fire season.

So what did the weather pattern look like for the end of that fire season? Well leading up to the end of the fire season, the upper-level pattern exhibited a large ridge parked right off the BC/WA coast with dry northwest flow over the region. Also, note the low-pressure area off the California Coast.

Early October 2012 500 mb pattern. 

So how does the pattern look for most of this week? Although it's far from identical, it does have some similarities, including the low near California, and the ridge over the Pacific Northwest.

500 mb pattern for Monday afternoon (10/5/15)

So what did the weather pattern that led to the end of the fire weather year in 2012 look like? The ridge broke down quite quickly and was replaced swift southwest flow into the Pacific Northwest and a deep low over the Gulf of Alaska. Again this brought cooler temperatures, periods of light rain (moderate in places), as well as significant cloud cover.

Mid-October 2012 500 mb pattern (Oct12-14)

How about this year? Is anything similar expected? Again although not a perfect match, there are some good similarities including a deep Gulf of Alaska low and deep southwest flow pointed into the Pacific Northwest from the eastern Pacific.

500 mb forecast for Oct 10, 2015

So how is our confidence in this solution and will this be the end of the fire season?  There are a few additional tools we can look at. One of the more interesting ones is called the NOMADS ensemble probability tool. This tool queries 21 GFS ensemble members or model runs and calculates the chances of any given parameter. Using this tool we can look at things such as what is our chance of seeing over a tenth of an inch of rain in a day?  When asking that particular question, here is the answer for the Grizzly Complex located over northern Shoshone County, ID.

The probability of seeing 0.10" of rain or more in 24 hrs over northern Shoshone County. 

So if you key in on the clustering of the blue bars, you can see that there is some consensus that by next weekend (10/10 and 10/11) that the weather pattern will support an increasing chance of rain (it peaks at 25% for the 24 hrs between 5pm Saturday through 5pm Sunday). Notice also that there is a small chance of light rain during the middle of the week.

Stay tuned and we shall see if this will truly be the end of a historically warm and dry fire season across the Inland Northwest.